You can rent a Toll-free number by logging in to your Plivo account and browsing through Plivo dashboard-> Phone Number-> Buy Number-> Toll-free or you can rent it using an API, please click here for more details. 

Note: all our Toll-free numbers are voice enabled by default. 

To add SMS functionality to the Toll-free number, the use case has to be qualified. Please click here and fill the form. Once you fill this form, our customer success team validates your use case and approves/declines it. If it is approved, our Support team will check the eligibility and provision your existing TFN for SMS(in case if you have rented it already). If the number cannot be provisioned for SMS our team will add a new Voice and SMS enabled number to your account. 

You can read more about Toll-free best practices and guidelines here.